GB2573338A

GB2573338A - Device

Info

Publication number: GB2573338A
Application number: GB1807383.3A
Authority: GB
Inventors: Kamtekar Kiran; Tobjörk Daniel
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 2018-05-04
Filing date: 2018-05-04
Publication date: 2019-11-06
Also published as: WO2019211623A1; GB201807383D0

Abstract

A fluorescent organic infrared light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and cathode wherein the light-emitting layer comprises polymer comprising a repeat unit of formula (I): wherein: R1 in each occurrence is independently a substituent; R2 and R3 in each occurrence is independently H or a substituent; and X in each occurrence is independently O or S. The polymer may be a copolymer comprising the repeat unit of formula (I) and one or more co-repeat units. The polymer may be used in the light-emitting layer in combination with a host material. Also shown is a method of forming an organic light emitting device and a composition comprising the polymer and a host material.

Description

The present invention relates to organic light emitting compositions and devices, particularly infra-red emitting organic light-emitting devices.

Background of the Invention

Electronic devices containing active organic materials include devices such as organic light emitting diodes (OLEDs), organic photoresponsive devices (in particular organic photovoltaic devices and organic photosensors), organic transistors and memory array devices. Devices containing active organic materials can offer benefits such as low weight, low power consumption and flexibility. Moreover, use of soluble organic materials allows use of solution processing in device manufacture, for example inkjet printing or spin-coating.

An OLED includes an anode, a cathode and one or more organic layers between the anode and cathode including at least one organic light-emitting layer.

Holes are injected into the device through the anode and electrons are injected through the cathode during operation of the device. Holes in the highest occupied molecular orbital (HOMO) and electrons in the lowest unoccupied molecular orbital (LUMO) of a lightemitting material combine to form an exciton that releases its energy as light.

A light emitting layer may comprise a semiconducting host material and a light-emitting dopant wherein energy is transferred from the host material to the light-emitting dopant. J. Appt. Phys. 65, 3610, 1989 discloses a host material doped with a fluorescent light-emitting dopant (that is, a light-emitting material in which light is emitted via decay of a singlet exciton).

Kang et al, Macromolecules, 1996, 29 (1), pp 165-169 discloses organic light-emitting diodes made from a blend of polymers.

OLEDs containing infrared emitting materials are also known as disclosed in, for example, Chuk-Lam Ho, Hua Li and Wai-Yeung Wong, “Red to near-infrared organometallic phosphorescent dyes for OLED applications”, J. Organomet. Chem. 751 (2014), 261-285.

US2017/0145030 discloses Polymer Compound A and the use thereof in an organic thin-film transistor:

Infrared emitting materials have a relatively small bandgap compared to materials emitting in the visible region. Consequently, efficiency of infrared materials can be low due to a high proportion of excitons decaying non-radiatively in accordance with the energy gap law.

It is therefore an object of the invention to provide fluorescent material having high efficiency infrared emission.

Summary of the Invention

In a first aspect the invention provides an organic infrared light-emitting device comprising an anode, a cathode and a light-emitting layer between the anode and cathode wherein the light-emitting layer comprises polymer comprising a repeat unit of formula (I):

(I) wherein:

R¹ in each occurrence is independently a substituent;

R in each occurrence is independently H or a substituent;

Q

R in each occurrence is independently H or a substituent; and

X in each occurrence is independently O or S.

In a second aspect, the invention provides a method of forming an organic light-emitting device according to the first aspect, the method comprising the step of depositing the lightemitting layer over one of the anode and cathode, and depositing the other of the anode and cathode over the light-emitting layer.

In a third aspect the invention provides a composition comprising a polymer comprising a repeat unit of formula (I) and a host material:

wherein:

R¹ in each occurrence is independently a substituent;

R in each occurrence is independently H or a substituent;

Q

R in each occurrence is independently H or a substituent; and

X in each occurrence is independently O or S.

In a fourth aspect the invention provides a solution comprising a composition according to the third aspect dissolved in one or more solvents.

Description of the Drawings

The invention will now be described in more detail with reference to the Figures, in which:

Figure 1 illustrates an OLED according to an embodiment; and

Figure 2 is a graph of normalised emission spectra of a device according to an embodiment in which the light-emitting layer consists of a polymer comprising a repeat unit of formula (I) and a device according to an embodiment in which the light-emitting layer consists of a polymer comprising a repeat unit of formula (I) and a host polymer.

Detailed Description of the Invention

Figure 1, which is not drawn to any scale, illustrates schematically an OLED 100 according to an embodiment. The OLED 100 is carried on substrate 107 and comprises an anode 101, a cathode 105 and a light-emitting layer 103 between the anode and the cathode. In other embodiments, the positions of the anode and cathode may be reversed, i.e. the cathode is the electrode on, or otherwise closest to, the substrate.

The light-emitting layer may consist of the polymer comprising a repeat unit of formula (I). Preferably, the light-emitting layer comprises the polymer comprising a repeat unit of formula (I) and a host material.

Further layers (not shown) may be provided between the anode and the cathode including, without limitation, hole-transporting layers, electron-transporting layers, hole-blocking layers, electron-blocking layers, hole-injection layers and electron-injection layers.

Exemplary OLED structures including one or more further layers include the following:

Anode / Hole-injection layer / Light-emitting layer / Cathode

Anode / Hole transporting layer / Light-emitting layer / Cathode

Anode / Hole-injection layer / Hole-transporting layer / Light-emitting layer / Cathode

Anode / Hole-injection layer / Hole-transporting layer / Light-emitting layer / Electrontransporting layer / Cathode

Anode / Hole-injection layer / Hole-transporting layer / Light-emitting layer / Electroninjecting layer / Cathode

Preferably, the device comprises one or both, more preferably both, of a hole-injection layer and a hole-transporting layer.

Preferably, the device comprises at least one of an electron-transporting layer and an electron injection layer.

In use, the device emits infrared fluorescent light from the light-emitting layer.

Preferably, the polymer comprising a repeat unit of formula (I) has a photoluminescent peak wavelength in the range of about more than 700 nm up to about 950 nm, optionally from about 7 fO nm, 720 nm or 750 nm up to about 830 nm or 850 nm.

Preferabty, tight-emitting iayer f03 is the oniy iayer of the device which emits light when in use.

The light-emitting layer comprises a polymer comprising a repeat unit of formula (I):

wherein:

R¹ in each occurrence is independently a substituent;

R in each occurrence is independently H or a substituent;

Q

R in each occurrence is independently H or a substituent; and

X in each occurrence is independently O or S.

Preferably, each X is S.

Optionally, each R¹ is independently selected from the group consisting of:

alkyl, optionally Ci_3o alkyl, wherein one or more non-adjacent, non-terminal carbon atoms may be replaced with optionally substituted aryl or heteroaryl, O, S, substituted N, C=O or -COO-, and one or more H atoms may be replaced with F; and aryl and heteroaryl groups, preferably C6-20 aryl groups, more preferably phenyl, which may be unsubstituted or substituted with one or more substituents.

Each R¹ is preferably a C1-30 alkyl group, more preferably a C10-30 alkyl group.

A “non-terminal carbon atom” of an alkyl group as used anywhere herein means a carbon atom other than the methyl group of a n-alkyl chain or the methyl groups of a branched alkyl chain.

Optionally, R and R are each independently in each occurrence selected from the group consisting of H; halogen, preferably F; CN; NO2; alkyl, optionally C1-20 alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted arylene or heteroarylene, O, S, substituted N, C=0 or -C00-, and one or more H atoms may be replaced with F; and aryl and heteroaryl groups, preferably C6-20 aryl groups, more preferably phenyl, which may be unsubstituted or substituted with one or more substituents.

Substituted N as described herein may be -NR¹⁰- wherein R¹⁰ is a substituent and is optionally a Ci_4o hydrocarbyl group, optionally a Ci_2o alkyl group.

In the case where R , R or R comprises an aryl(ene) or heteroaryl(ene), any substituents of the aryl(ene) or heteroaryl(ene) are optionally selected from C1-12 alkyl groups wherein one or more non-adjacent, non-terminal C atoms of the alkyl group may be replaced with 0, S, C=0, or COO and one or more H atoms of the alkyl group may be replaced with F.

Each R is preferably H.

Q

Each R is preferably H.

The polymer may be a homopolymer, or a copolymer comprising the repeat unit of formula (I) and one or more co-repeat units.

Repeat units of formula (I) preferably make up 1-99 mol %, optionally 10-90 mol % of the repeat units of a copolymer.

Optionally, co-repeat units are selected from C6-20 arylene co-repeat units and heterarylene co-repeat units comprising 5-20 heteroaromatic ring atoms. The or each co-repeat unit may be unsubstituted or substituted with one or more substituents.

Preferably, the co-polymer comprises a repeat unit of formula (II):

(Π) wherein Υ in each occurrence is independently N or CR⁴ and R⁴ is H or a substituent,

3 preferably H or a substituent as described above for substituent groups R and R . Most preferably, R⁴ is H, F or Ci_2o alkyl.

Optionally, Cf,-2o arylene co-repeat units are selected from formulae (III) - (VI):

(R⁷)t uk (III)

(V) (VI) wherein t in each occurrence is independently 0, 1, 2, 3 or 4, preferably 1 or 2; R independently in each occurrence is a substituent; s in each occurrence is independently 0, 1

Q or 2, preferably 0 or 1; and R independently in each occurrence is a substituent wherein two

Q

R groups may be linked to form an unsubstituted or substituted ring.

8

Where present, each R and R may independently be selected from the group consisting of:

alkyl, optionally C1-20 alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl, O, S, substituted N, C=O or COO-, and one or more H atoms may be replaced with F;

aryl and heteroaryl groups, preferably C6-20 aryl groups, more preferably phenyl, that may be unsubstituted or substituted with one or more substituents; and a linear or branched chain of aryl or heteroaryl groups, preferably C6-20 aryl groups, more preferably phenyl, each of which groups may independently be substituted, optionally a group of formula -(Ar )_v wherein each Ar is independently an aryl or heteroaryl group and v is at least 2, preferably a branched or linear chain of phenyl groups.

8

In the case where R or R comprises an aryl or heteroaryl group, or a linear or branched chain of aryl or heteroaryl groups, the or each aryl or heteroaryl group may be substituted with one or more substituents R⁶ selected from the group consisting of:

alkyl, for example C1-20 alkyl, wherein one or more non-adjacent C atoms may be replaced with O, S, substituted N, C=0 and -COO- and one or more H atoms of the alkyl group may be replaced with F;

NR⁹2, OR⁹, SR⁹, SiR⁹ ₃ and fluorine, nitro and cyano;

wherein each R⁹ is independently selected from the group consisting of alkyl, preferably C1-20 alkyl; and aryl or heteroaryl, preferably phenyl, optionally substituted with one or more Ci_2o alkyl groups.

Preferred substituents of aryl or heteroaryl groups of R or R are selected from C1-20 alkyl.

Q

In the case where two groups R form a ring, the one or more substituents of the ring, if present, are optionally selected from Ci_2o alkyl groups.

Preferably, each R , where present, and R is independently selected from Ci_4ohydrocarbyl. Preferred Cmo hydrocarbyl groups are C1-20 alkyl; unsubstituted phenyl; phenyl substituted with one or more C1-20 alkyl groups; and a linear or branched chain of phenyl groups, wherein each phenyl may be unsubstituted or substituted with one or more Ci_2o alkyl groups.

Host

The light-emitting layer may be a composition comprising or consisting of a polymer comprising a repeat unit of formula (I) and at least one host material.

The weight ratio of the one or more host materials : the polymer comprising a repeat unit of formula (I) is preferably greater than 1:1, preferably at least 2:1,3:1 or 4:1.

Preferably, the host material has a higher photoluminescent quantum yield (PLQY) and shorter peak wavelength than the infrared emitting material.

Optionally, the host material has a photoluminescent peak wavelength that is shorter than that of the polymer comprising a repeat unit of formula (I), preferably no more than about 250 nm, preferably no more than about 200 nm or about 150 nm.

Optionally, the difference in PLQY of the first and second materials is at least 20%, optionally at least 30%, 40% or 50%.

Optionally, the host material has a peak wavelength in the range of 400-680 nm, preferably 500-650 nm.

Optionally, host material: polymer comprising a repeat unit of formula (I) weight ratio is in the range of about 99 : 1 - 60 : 40, preferably 95 : 5 - 70 : 30.

Optionally, the composition has a peak wavelength of at least 690 nm, preferably at least 700 nm. Optionally, the composition has a peak wavelength of up to about 900 nm, optionally 850 nm or 800 nm.

The host material may be polymeric or non-polymeric. Preferably, the host material is polymeric. The host material may be conjugated or non-conjugated, preferably conjugated.

The host polymer preferably comprises at least one of a repeat unit comprising at least one heteroarylene group and a repeat unit comprising an arylamino group. The host polymer preferably further comprises one or more arylene co-repeat units, optionally one or more arylene repeat units selected from formulae (III)-(VI).

Optionally, the host polymer comprises one or more repeat units selected from repeat units of formula (II) as described above and repeat units of formula (VII), (VIII) or (IX):

(νπ)

(Ar⁸)d---Ν—(Ar⁹)e

R¹³

Ν—(Ar¹⁰)₍

R¹³

(VIII) (IX)

With reference to formula (VII), R³ and R⁴ are as described above.

With reference to formula (VIII), Ar³ and Ar⁴ are each a C6-20 arylene group, preferably phenylene, and Ar⁵ is a Ce-20 aryl group, preferably phenyl. Ar³, Ar⁴ and Ar⁵ are each independently unsubstituted or substituted with one or more substituents.

Optionally, substituents of Ar³ and Ar⁴ are selected from CN; NO2; and Ci_2o alkyl wherein one or more non-adjacent, non-terminal C atoms of the alkyl group may be replaced with O, S, NR or SiR 2, COO or CO; wherein R in each occurrence is a C1-20hydrocarbyl group, optionally a C1-12 alkyl group, unsubstituted phenyl, or phenyl substituted with one or more alkyl groups.

Optionally, substituents of Ar⁵ are selected from CN; NO2; Ci_2o alkyl wherein one or more

Q non-adjacent, non-terminal C atoms of the alkyl group may be replaced with O, S, NR or

Q

SiR 2, COO or CO; phenyl which is unsubstituted or substituted with one or more substituents; and pyridyl which is unsubstituted or substituted with one or more substituents. Substituents of phenyl or pyridyl, if present, may be selected from C1-12 alkyl.

With reference to formula (IX), Ar⁸, Ar⁹ and Ar¹⁰ in each occurrence are independently selected from substituted or unsubstituted aryl or heteroaryl, g is 0, 1 or 2, preferably 0 or 1,

R independently in each occurrence is a substituent, and d, e and f are each independently 1, 2 or 3.

R , which may be the same or different in each occurrence when g is 1 or 2, is preferably selected from the group consisting of alkyl, optionally C1-20 alkyl, Ar¹¹ and a branched or linear chain of Ar¹¹ groups wherein Ar¹¹ in each occurrence is independently substituted or unsubstituted aryl or heteroaryl.

Any two aromatic or heteroaromatic groups selected from Ar⁸, Ar⁹, and, if present, Ar¹⁰ and Ar¹¹ that are directly bound to the same N atom may be linked by a direct bond or a divalent linking atom or group. Preferred divalent linking atoms and groups include O, S; substituted N; and substituted C.

Ar and Ar are preferably C6-20 aryl, more preferably phenyl, which may be unsubstituted or substituted with one or more substituents.

In the case where g = 0, Ar⁹ is preferably C6-20 aryl, more preferably phenyl, that may be unsubstituted or substituted with one or more substituents.

In the case where g = 1, Ar⁹ is preferably C6-20 aryl, more preferably phenyl or a polycyclic aromatic group, for example naphthalene, perylene, anthracene or fluorene, that may be unsubstituted or substituted with one or more substituents.

R¹³ is preferably Ar¹¹ or a branched or linear chain of Ar¹¹ groups. Ar¹¹ in each occurrence is preferably phenyl that may be unsubstituted or substituted with one or more substituents.

Exemplary groups R include the following, each of which may be unsubstituted or substituted with one or more substituents, and wherein * represents a point of attachment to

N:

d e and f are preferably each 1.

Ar⁸, Ar⁹, and, if present, Ar¹⁰ and Ar¹¹ are each independently unsubstituted or substituted with one or more, optionally 1, 2, 3 or 4, substituents. Exemplary substituents may be selected from substituted or unsubstituted alkyl, optionally C1-20 alkyl, wherein one or more non-adjacent C atoms may be replaced with optionally substituted aryl or heteroaryl (preferably phenyl), O, S, C=0 or -COO- and one or more H atoms may be replaced with F.

Preferred substituents of Ar⁸, Ar⁹, and, if present, Ar¹⁰ and Ar¹¹ are Ci_4o hydrocarbyl, preferably C1-20 alkyl.

Preferred repeat units of formula (IX) include unsubstituted or substituted units of formulae (IX-1), (IX-2) and (IX-3):

2 3

Preferably, the polymer comprising a repeat unit of formula (I) does not comprise a transition metal complex.

Polymers as described herein, including but not limited to host polymers and polymers comprising a repeat unit of formula (I), may have a polystyrene-equivalent number-average molecular weight (Mn) measured by gel permeation chromatography in the range of about 3x10 to 1x10 , and preferably 1x10 to 5x10 . The polystyrene-equivalent weight-average molecular weight (Mw) of the polymers described herein may be 1x10 to 1x10 , and preferably lx 10⁴ to lx 10⁷.

Polymers as described herein are preferably amorphous.

Charge transporting and charge blocking layers

A hole transporting layer may be provided between the anode of an OLED and the lightemitting layer.

An electron transporting layer may be provided between the cathode of an OLED and the light-emitting layer.

An electron blocking layer may be provided between the anode and the light-emitting layer.

A hole blocking layer may be provided between the cathode and the light-emitting layer.

Transporting and blocking layers may be used in combination. Depending on its HOMO and LUMO levels, a single layer may both transport one of holes and electrons and block the other of holes and electrons.

A charge-transporting layer or charge-blocking layer may be crosslinked, particularly if a layer overlying that charge-transporting or charge-blocking layer is deposited from a solution containing a solvent capable of dissolving one or more materials of the charge-transporting or charge-blocking layer. The crosslinkable group used for this crosslinking may be a crosslinkable group comprising a reactive double bond such and a vinyl or acrylate group, or a benzocyclobutane group. The crosslinkable group may be provided as a substituent pendant from the backbone of a charge-transporting or charge-blocking polymer. Following formation of a charge-transporting or charge blocking layer, the crosslinkable group may be crosslinked by thermal treatment or irradiation.

If present, a hole transporting layer located between the anode and the light-emitting layer preferably contains a hole-transporting material having a HOMO level of less than or equal to 5.5 eV, more preferably around 4.8-5.5 eV as measured by square wave voltammetry. The HOMO level of the hole transporting material of the hole-transporting layer may be selected so as to be within 0.2 eV, optionally within 0.1 eV, of the HOMO of a component of the light-emitting layer in order to provide a small barrier to hole transport.

A hole-transporting material of a hole-transporting polymer may be a polymer comprising a repeat unit of formula (IX) as described herein, optionally a homopolymer of a repeat unit of formula (IX) or a copolymer comprising a repeat unit of formula (IX) and one or more corepeat units, optionally one or more arylene co-repeat units as described herein. One or more repeat units of such a hole-transporting polymer may be substituted with a crosslinkable group, optionally a crosslinkable double bond group and / or a crosslinkable benzocyclobutane group, that may be crosslinked following deposition of the holetransporting polymer to form the hole-transporting layer.

If present, an electron transporting layer located between the light-emitting layers and cathode preferably has a LUMO level of around 2.5-3.5 eV as measured by square wave voltammetry.

An electron transporting layer may contain a polymer comprising a chain of optionally substituted arylene repeat units, such as a chain of fluorene repeat units.

Hole ini ection layers

A conductive hole injection layer, which may be formed from a conductive organic or inorganic material, may be provided between the anode and the light-emitting layer or layers to assist hole injection from the anode into the layer or layers of semiconducting polymer. A hole transporting layer may be used in combination with a hole injection layer.

Examples of doped organic hole injection materials include optionally substituted, doped poly(ethylene dioxythiophene) (PEDT), in particular PEDT doped with a charge-balancing polyacid such as polystyrene sulfonate (PSS) as disclosed in EP 0901176 and EP 0947123, polyacrylic acid or a fluorinated sulfonic acid, for example Nafion ®; polyaniline as disclosed in US 5723873 and US 5798170; and optionally substituted polythiophene or poly(thienothiophene). Examples of conductive inorganic materials include transition metal oxides such as VOx, MoOx and RuOx as disclosed in Journal of Physics D: Applied Physics (1996),29(11),2750-2753.

Cathode

The cathode is selected from materials that have a work function allowing injection of electrons into the light-emitting layer or layers.

The cathode may consist of a single material such as a layer of aluminium. The cathode may comprise a plurality of metals, for example a bilayer such as calcium and aluminium as disclosed in WO 98/10621. The cathode may contain or consist of a layer of silver, for example a bilayer of silver and aluminium. Inclusion of a layer of silver is particularly advantageous due to its high reflectivity of infrared wavelengths. The cathode may contain a layer containing elemental barium, for example as disclosed in WO 98/57381, Appl. Phys. Lett. 2002, 81(4), 634 and WO 02/84759 or a layer containing elemental magnesium. The cathode may contain a thin (e.g. 1-5 nm thick) layer of metal compound between the light emitting layer(s) of the OLED and one or more conductive layers of the cathode, such as one or more metal layers. Exemplary metal compounds include an oxide or fluoride of an alkali or alkali earth metal to assist electron injection, for example lithium or sodium fluoride as disclosed in WO 00/48258; barium fluoride as disclosed in Appl. Phys. Lett. 2001, 79(5), 2001; and barium oxide. In order to provide efficient injection of electrons into the device, the cathode preferably has a work function of less than 3.5 eV, more preferably less than 3.2 eV, most preferably less than 3 eV. Work functions of metals can be found in, for example, Michaelson, J. Appl. Phys. 48(11), 4729, 1977.

Layer formation

The light-emitting layer described herein is preferably formed by deposition from a formulation comprising the polymer comprising the repeat unit of formula (I) dissolved in one or more organic solvents, and any other components of the light-emitting layer dissolved or dispersed in the solvent or solvents.

Suitable solvents include, without limitation, benzenes with one or more alkyl or alkoxy substituents such as toluene, xylene, anisole and mixtures thereof.

Exemplary solution deposition techniques include printing and coating techniques such spincoating, dip-coating, roll-to-roll coating or roll-to-roll printing, doctor blade coating, slot die coating, gravure printing, flexographic printing, dispense printing, screen printing and inkjet printing.

In inkjet printing, ink is deposited in a region on a surface by depositing discrete droplets ejected from an inkjet print head.

In dispense printing, ink is deposited as a continuous stream of ink from a nozzle.

Solution deposition methods may be used to form other layers of an OLED including (where present) a hole injection layer, a charge transporting layer and a charge blocking layer.

Applications

An organic infrared light-emitting diode as described herein may be used, without limitation, in night vision goggles, sensors, for example pulse oximeters, and CMOS chips. A sensor may comprise one or more OLEDs as described herein and at least one photodetector device, the or each photodetector device being configured to detect emission from the one more OLEDs. Optionally, the OLED of a sensor, preferably the OLED of a wearable sensor, has an operating voltage of no more than 5V.

Examples

Measurements

Photoluminescent peak values and PLQY values as described herein were measured in an integrating sphere connected to Hamamatsu C9920-02 with a xenon lamp L8474and a monochromator for choice of exact wavelength. Samples were with prepared by spin-coating a film of the fluorescent polymer or composition onto a quartz disk.

Materials

Infrared Polymer 1

Comparative Infrared Polymer 1

Host Polymer 1 ; γ_; ^8^17 ^8^17 Ν /Ν

S

Host Polymer 2 was formed by Suzuki polymerisation as disclosed in WO 00/53656 of the following monomers:

mol %

Photoluminescence

Photoluminescence of infrared polymers and compositions as set out in Table 1 were measured.

Table 1

	Ratio (wt %)	PLQY (%)	Emission peak wavelength (nm)
Infrared Polymer 1	-	23	750-766
Host Polymer 1	-	76.5	561
Composition Example 1	Host Polymer 1 (90) : Infrared Polymer 1 (10)	46.3	725-731
Composition Example 2	Host Polymer 1 (80) : Infrared Polymer 1 (20)	40	728-737
Comparative Infrared Polymer 1	-	4%	731
Comparative Composition 1	Host Polymer 1 (90) : Comparative Infrared Polymer 1 (10)	31.8%	720
Comparative Composition 2	Host Polymer 1 (80) : Comparative Infrared Polymer 1 (20)	22.4%	725

Infrared Polymer 1 has a higher photoluminescent quantum yield (PLQY) than Comparative

Infrared Polymer 1 both on its own and as part of a composition with a host polymer.

Device Examples 1 and 2

Infrared emitting OLEDs having the following structure were formed on a glass substrate:

ITO / HIL (65 nm) / HTL (22 nm) / LEL (70 nm) / ETL (40 nm) / Cathode in which ITO is an indium tin oxide anode; HIL is a hole-injection layer; HTL is a holetransporting layer; LEL is an infrared light-emitting layer; and ETL is an electrontransporting layer.

To form the device, the ITO was baked and treated with UV and ozone and the hole injection layer was then formed by spin-coating an aqueous formulation of a hole-injection material available from Nissan Chemical Industries onto the ITO and heating the resultant layer at 180°C for 15 minutes in air. The hole transporting layer was formed by spin-coating a holetransporting polymer comprising fluorene and amine repeat units as described in WO 2013/108022, the contents of which are incorporated herein by reference, from o-xylene solution and crosslinking the polymer by heating in a glovebox in a nitrogen atmosphere at 190°C (as measured for the device layer in contact with the heated surface, e.g. glass substrate) for 60 minutes. The light-emitting layer was formed by spin-coating the material or materials of the light-emitting layer as set out in Table 2 from o-xylene solution. An electron-transporting layer was formed by spin-coating an electron-transporting polymer substituted with a Cs salt as disclosed in WO 2012/133229 and n-dopant 1 from methanol solution in a glovebox in a nitrogen atmosphere followed by baking at 160°C for 10 minutes. The cathode was formed by evaporation of a first layer of aluminium (100 nm) and a second layer of silver (100 nm). The completed devices were encapsulated.

€)

n-dopant 1

As set out in Table 2 and as shown in Figure 2, much higher external quantum efficiency and radiant power are achieved, with a slight shifting of the peak wavelength to a shorter wavelength, when the light-emitting polymer is used in combination with a host polymer. A small amount of emission attributed to the host polymer (-550-600 nm) was observed for Device Example 2.

Table 2

Device	Lightemitting layer	J (mA/cm²)	EQE (%)	V (V)	Rad Power (mW/cm²)	Wavelength (nm)
Device Example 1	Polymer Example 1	50	0.2	2.9	0.2	732
Device Example 2	Host Polymer 2: Polymer Example 1 9:1 by weight	50	0.8	3.8	0.72	720

Device Example 3

A device was prepared as described for Device Example 1 except that the light-emitting layer was formed to a thickness of 50 nm from Composition Example 1 and n-dopant 1 was not included in the electron-transporting layer.

Device Example 4

A device was prepared as described for Device Example 3 except that the light-emitting layer was formed to a thickness of 70 nm

With reference to Table 3, slightly higher efficiency and radiant power was achieved at a light-emitting layer thickness of 70 nm as compared to 50 nm.

With reference to Figure 2, a higher radiant power was maintained at a current density of 50 mA/cm .

Table 3

Device

Emissive layer

J (mA/cm2)

EQE (%)

V

Rad power

Wavelength

	thickness (nm)			(V)	(mW/cm2)	(nm)
Device Example 3	50	50	1.93	3.13	1.72	719
Device Example 4	70	50	1.99	3.25	1.73	719

Although the present invention has been described in terms of specific exemplary embodiments, it will be appreciated that various modifications, alterations and/or combinations of features disclosed herein will be apparent to those skilled in the art without departing from the scope of the invention as set forth in the following claims.

Claims

1. An organic infrared light-emitting device comprising an anode, a cathode and a lightemitting layer between the anode and cathode wherein the light-emitting layer comprises polymer comprising a repeat unit of formula (I):

(I) wherein:

R¹ in each occurrence is independently a substituent;

R² in each occurrence is independently H or a substituent;

Q

R in each occurrence is independently H or a substituent; and

X in each occurrence is independently 0 or S.

2. An organic infrared light-emitting device according to claim 1 wherein each X is S.

3. An organic infrared light-emitting device according to claim 1 or 2 wherein each R¹ is independently selected from the group consisting of:

alkyl wherein one or more non-adjacent, non-terminal C atoms may be replaced with optionally substituted aryl or heteroaryl, O, S, substituted N, C=0 or -C00-, and one or more H atoms may be replaced with F; and an aryl or heteroaryl which may be unsubstituted or substituted with one or more substituents.

4. An organic infrared light-emitting device according to claim 3 wherein each R¹ is a Ci-30 alkyl group.

5. An organic infrared light-emitting device according to any one of the preceding claims wherein R and R are each independently in each occurrence selected from the group consisting of H; F; CN; NO2; alkyl wherein one or more non-adjacent C atoms may be replaced with optionally substituted arylene or heteroarylene, O, S, substituted N, C=0 or -C00-, and one or more H atoms may be replaced with F; and aryl and heteroaryl groups which may be unsubstituted or substituted with one or more substituents.

6. An organic infrared light-emitting device according to claim 5 wherein each R is H.

Q

7. An organic infrared light-emitting device according to claim 5 or 6 wherein each R is H.

8. An organic infrared light-emitting device according to any one of the preceding claims wherein the polymer comprising the repeat unit of formula (I) is a copolymer comprising one or more co-repeat units.

9. An organic infrared light-emitting device according to claim 8 wherein the or each corepeat units are selected from C6-20 arylene co-repeat units and heterarylene co-repeat units comprising 5-20 heteroaromatic ring atoms, each of which may be unsubstituted or substituted with one or more substituents.

10. An organic infrared light-emitting device according to claim 9 wherein the polymer comprising a repeat unit of formula (I) comprises a co-repeat unit of formula (II):

(Π) wherein Y in each occurrence is independently N or CR⁴ and R⁴ is H or a substituent.

11. An organic infrared light-emitting device according to any one of the preceding claims, wherein the light-emitting layer comprises a host material.

12. An organic infrared light-emitting device according to claim 11, wherein host material has a higher photoluminescent quantum yield than the polymer comprising the repeat unit of formula (I).

13. A method of forming an organic light-emitting device according to any one of the preceding claims comprising the step of depositing the light-emitting layer over one of the anode and cathode, and depositing the other of the anode and cathode over the light-emitting layer.

14. A method according to claim 13 wherein the light-emitting layer is deposited from a formulation comprising the components of the light-emitting layer dissolved or dispersed therein.

15. A composition comprising a polymer comprising a repeat unit of formula (I) and a host material:

wherein:

R¹ in each occurrence is independently a substituent;

R in each occurrence is independently H or a substituent;

□

R in each occurrence is independently H or a substituent; and

X in each occurrence is independently 0 or S.

16. A solution comprising a composition according to claim 15 dissolved in one or more solvents.